In electrical-discharge machining, in which electrical discharge is generated between a machining electrode and a workpiece facing each other (hereinafter, “gap”) and machining proceeds by melting and removing the workpiece by the generated thermal energy, water-based and oil-based machining fluid have been used for cooling of the electrical discharge point and ion quenching and dielectric recovery after generation of electrical discharge.
In an electrical-discharge machining device using water-based machining fluid, especially pure water, a filter device that separates machining debris, an ion-exchange resin that maintains the specific resistance of the electrical-discharge machining fluid, and the like are provided in order to clean the electrical-discharge machining fluid.
In an electrical-discharge machining device using oil-based machining fluid, a filter device that separates machining debris is also provided. For example, a filter device that uses grain-refined activated white earth as a machining-debris adhering agent is known (for example, see Patent Literature 1). It is known that, in order to stabilize the electrical discharge state by reducing the generated amount of metal machining debris in the oil-based machining fluid or decreasing the particle size, a metal complex is formed by adding a complexing agent to oil-based machining fluid. A technique has been proposed in which a molecular sieve for removing water that separates the complexing agent and oil content in the oil-based machining fluid is provided, thereby improving the electrical discharge performance (for example, see Patent Literature 2). However, a device that maintains the specific resistance of the electrical-discharge machining fluid in the electrical-discharge machining device that uses oil-based machining fluid has not been considered heretofore, and such a device has not been proposed yet.